Papers by Marta Iglesias-Julios
Prosocial third-party punishment (3PP) is a punitive behavior against antisocial individuals, whi... more Prosocial third-party punishment (3PP) is a punitive behavior against antisocial individuals, which might explain extended cooperativeness in humans. 3PP shows sexual dimorphism, being more frequent in men than in women. We studied whether sexually dimorphic features related to sexual hormones during development (facial dimorphism and 2D:4D) influence the tendency to engage in 3PP in a sample of 511 women and 328 men. After playing a Prisoner's Dilemma, participants had to decide whether to penalize the defection of a third player who had exploited his/her counterpart's cooperation. In line with previous studies, we observe that men are more prone to engage in 3PP than women. We find that this sex difference is due to cooperative men being more likely to punish than cooperative women. In addition, men with higher facial masculinity are less likely to engage in 3PP, whereas no features influence 3PP in women. We discuss the possibility that sex differences in the motivations and fitness implications underlying 3PP might be driving the observed results. Third party punishment (3PP) is a behavior costly to the individual exerting it and aimed at penalizing individuals who have not directly interacted with the punisher. It is considered to be altruistic when individuals exert it to penalize others' harmful behavior 1. Altruistic 3PP appears in many human societies 2-4. Because of that, it has been proposed as one among the possible explanations for extended human cooperation 1,5,6 , as individuals who engage in altruistic 3PP pay currently a cost to increase social welfare. Still, for altruistic 3PP to be selected for, it must improve the inclusive fitness of individuals exerting it 7 ; either directly (i.e. increasing reproductive success through processes linked to reciprocity or reputation) or indirectly 8-11. In fact, the attainment of such fitness benefits must be the ultimate cause of prosocial behavior 7,12,13 , independently of whether the individual receives in exchange future social advantages or an improvement in resources. From this viewpoint, altruistic 3PP is expected to share proximal and evolutionary motivations and influences with other forms of prosociality. Individuals who engage in altruistic 3PP should behave prosocially in different contexts 4 , assuming that the tendency to behave prosocially carries over different situations 2,14-18 , and across time 14,19,20. Developmental and physiological features have been found to influence cooperation 21-25 , trustworthiness 26 and spontaneous generosity 27. Thus, it is likely that 3PP is also influenced by these features, which seem to link the genetic propensity to behave prosocially, established throughout the evolutionary process 7,28 , to actual prosoci-ality. Genes, jointly with the developmental environment, affect various biological features that in turn influence behavior. These features include hormonal levels, specific neural properties or preconfigured neural circuits, and even physiological features not directly related to behavior but with an indirect impact on it. Sex has been the only biological variable previously studied in relation to 3PP: it has been shown that men and women engage in 3PP with different intensity, with men punishing more harshly than women 15,29,30. On the other hand, meta-analyses show that there is no such sexual dimorphism in cooperative behavior 31,32 , indicating that the relationship between cooperation and 3PP might be more complex than previously thought. Among the physiology-related variables with a likely influence on 3PP, those related to cooperation are good candidates 21-25 given the described association between altruistic 3PP and the tendency to cooperate 33-35. Interestingly, some of these variables are sexually dimorphic 36,37 , or show differential impacts on cooperation by
Most animals fight by repeating complex stereotypic behaviours, yet the internal structure of the... more Most animals fight by repeating complex stereotypic behaviours, yet the internal structure of these behaviours has rarely been dissected in detail. We characterized the internal structure of fighting behaviours by developing a machine learning pipeline that measures and classifies the behaviour of individual unmarked animals on a sub-second time scale. This allowed us to quantify several previously hidden features of zebrafish fighting strategies. We found strong correlations between the velocity of the attacker and the defender, indicating a dynamic matching of approach and avoidance efforts. While velocity matching was ubiquitous, the spatial dynamics of attacks showed phase-specific differences. Contest-phase attacks were characterized by a paradoxical sideways attraction of the retreating animal towards the attacker, suggesting that the defender combines avoidance manoeuvres with display-like manoeuvres. Post-resolution attacks lacked display-like features and the defender was avoidance focused. From the perspective of the winner, game-theory modelling further suggested that highly energetically costly post-resolution attacks occurred because the winner was trying to increase its relative dominance over the loser. Overall, the rich structure of zebrafish motor coordination during fighting indicates a greater complexity and layering of strategies than has previously been recognized.
Attractiveness plays an important role in social exchange and in the ability to attract potential... more Attractiveness plays an important role in social exchange and in the ability to attract potential mates, especially for women. Several facial traits have been described as reliable indicators
of attractiveness in women, but very few studies consider the influence of several measurements simultaneously. In addition, most studies consider just one of two assessments to directly measure attractiveness: either self-evaluation or men's ratings. We explored the relationship between these two estimators of attractiveness and a set of facial traits in a sample of 266 young Spanish women. These traits are: facial fluctuating asymmetry,
facial averageness, facial sexual dimorphism, and facial maturity. We made use of the advantage of having recently developed methodologies that enabled us to measure these
variables in real faces.We also controlled for three other widely used variables: age, body mass index and waist-to-hip ratio. The inclusion of many different variables allowed us to detect any possible interaction between the features described that could affect attractiveness perception. Our results show that facial fluctuating asymmetry is related both to selfperceived and male-rated attractiveness. Other facial traits are related only to one direct attractiveness measurement: facial averageness and facial maturity only affect men's ratings.
Unmodified faces are closer to natural stimuli than are manipulated photographs, and therefore our results support the importance of employing unmodified faces to analyse the
factors affecting attractiveness. We also discuss the relatively low equivalence between self-perceived and male-rated attractiveness and how various anthropometric traits are relevant to them in different ways. Finally, we highlight the need to perform integrated-variable studies to fully understand female attractiveness.
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Papers by Marta Iglesias-Julios
of attractiveness in women, but very few studies consider the influence of several measurements simultaneously. In addition, most studies consider just one of two assessments to directly measure attractiveness: either self-evaluation or men's ratings. We explored the relationship between these two estimators of attractiveness and a set of facial traits in a sample of 266 young Spanish women. These traits are: facial fluctuating asymmetry,
facial averageness, facial sexual dimorphism, and facial maturity. We made use of the advantage of having recently developed methodologies that enabled us to measure these
variables in real faces.We also controlled for three other widely used variables: age, body mass index and waist-to-hip ratio. The inclusion of many different variables allowed us to detect any possible interaction between the features described that could affect attractiveness perception. Our results show that facial fluctuating asymmetry is related both to selfperceived and male-rated attractiveness. Other facial traits are related only to one direct attractiveness measurement: facial averageness and facial maturity only affect men's ratings.
Unmodified faces are closer to natural stimuli than are manipulated photographs, and therefore our results support the importance of employing unmodified faces to analyse the
factors affecting attractiveness. We also discuss the relatively low equivalence between self-perceived and male-rated attractiveness and how various anthropometric traits are relevant to them in different ways. Finally, we highlight the need to perform integrated-variable studies to fully understand female attractiveness.
of attractiveness in women, but very few studies consider the influence of several measurements simultaneously. In addition, most studies consider just one of two assessments to directly measure attractiveness: either self-evaluation or men's ratings. We explored the relationship between these two estimators of attractiveness and a set of facial traits in a sample of 266 young Spanish women. These traits are: facial fluctuating asymmetry,
facial averageness, facial sexual dimorphism, and facial maturity. We made use of the advantage of having recently developed methodologies that enabled us to measure these
variables in real faces.We also controlled for three other widely used variables: age, body mass index and waist-to-hip ratio. The inclusion of many different variables allowed us to detect any possible interaction between the features described that could affect attractiveness perception. Our results show that facial fluctuating asymmetry is related both to selfperceived and male-rated attractiveness. Other facial traits are related only to one direct attractiveness measurement: facial averageness and facial maturity only affect men's ratings.
Unmodified faces are closer to natural stimuli than are manipulated photographs, and therefore our results support the importance of employing unmodified faces to analyse the
factors affecting attractiveness. We also discuss the relatively low equivalence between self-perceived and male-rated attractiveness and how various anthropometric traits are relevant to them in different ways. Finally, we highlight the need to perform integrated-variable studies to fully understand female attractiveness.